Modern mobile communication systems provide a variety of services to mobile device users. Such systems often provide advertising and social network services based on location information of the mobile device users. Location information of a user's mobile device may allow a service provider to infer a user's environment and offer more targeted advertising and social network services to the user. In addition, location information of mobile devices in nearby locations or similar types of locations may allow the service provider to provide information on users located in similar environments.
One of the conventional methods determines the locations of mobile devices by using GPS (Global Positioning System). Unfortunately, GPS is often unavailable in many locations where mobile devices are used. For example, when the mobile devices are located in buildings or indoor situations, location information through GPS may not be available. In addition, GPS may not accurately distinguish between users in different vertical locations such as a user on one floor and another user on another floor.
Another conventional method determines locations of mobile devices by sensing ambient sounds of the mobile devices. Unfortunately, such a method may not be accurate in determining the locations or types of locations of the mobile devices due to artifacts. For example, when a user touches, taps, or even softly rubs his or her mobile device, the mobile device typically captures an artifact sound signal associated with such an activity. In addition, when a mobile device is in a pocket or bag of the user, the microphone of the mobile device may capture artifact noises.
Such artifacts are generally unique to an individual mobile device and are not detected by other mobile devices. As a result, the artifacts may prevent accurate identification of mobile devices in a similar sound environment and degrade the accuracy in determining the location information of the mobile devices.